Dynamic loud speaker unit



Jan. 24, 1933. H, 1 FANGER 1,895,071

DYNAMIC LOUD SPEAKER UNIT Filed Sept. 25, 1928 MEM-0@ Herma/7 J fnger Patented Jan. 24, 1933 UNITED STATES HERMAN .T. FANGER, OF OAKLAND, CALIFORNIA DYNAMIC LOUD lSPEAKER UNIT Application filed September 25, 1928.

This invention relates to devices for transforming signal carrying electrical impulses into sound waves; and more particularly to a device employing the dynamic principle whereby a movable conductor is actuated in accordance with the signals to be reproduced.

Such units employ a magnetic field, usually produced by the aid of'a fieldcoil supplied with direct current. The magnetic circuit includes a small gap in which a coil or other conductor is movable, in such manner that the movement cuts the magnetic lines of force. When such a conductor is supplied with current carrying the impulses, this current reacts with the transverse field to move the coil, and this movement can be used to actuate an airfactuator, such as a diaphragm or a cone.

The field coil, in order to secure good efti- 0 ciency, must be supplied with a considerable energizing current, sometimes of the order of an ampere. In prior devices, the heat losses in the coil serves to heat the coil and the surrounding parts of the structure; and it is obvious that this heating must be taken care of by proper circulation so that it may not adect the unit deleteriously.

It is one of the objects of my invention to prevent this undesirable temperature rise, and more particularly by providing a large radiating surface for the structure. I accomplish this result by so arranging the magnetic circuit that it has, in addition to an external radiating surface, a supplemental interior radiating surface. Accordingly, it is another object of my invention to provide a structure for the magnetic circuit that accomplishes these useful results.

` In dynamic speakers of the prior art, the magnetic field set up by the moving conductor has a reaction on the core of the field coil, causing eddy currents therein; this reaction may produce and often does produce, distortion in the reproduction. It is another object of my invention to neutralize this effect. More particularly, I utilize a special form of coil that has no appreciable magnetic effect on the core. For example, I can use a pair of moving coil sections, supplied with Serial No. 308,152.

current in such a way that the combined magnetic effect is substantially zero.

In a single coil device, itis evident that movement of the coil in response to signaling impulses may serve partly to remove the coil from the influence of the field, and the response for a large coil movement is materially lessened. In my two coil arrangement, this effect is nicely overcome, for as one coil moves out of the field, the other can move into the field. Furthermore, the effect of the coils on the air actuator is cumulative, to produce a push-pull result. Y

It is often desirable to provide a speaker that embodies a horn as well as a cone, so that all tones of the signals can be faithfully re produced. It is another object of my invention to provide a single unit in which the horn and cone are both actuated thereby, and particularly by using the cone as the mouth for the diaphragm.

My invention possesses many other advantages, and has other objects which may be made more easily apparent from a consideration of an embodiment of my invention. For this purpose I have shown a form in the drawing accompanyingand forming part of the present specification. I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawing: 35

Figure l is a sectional View, mainly diagrammatic, of a loud speaker unit embodying my invention; and

Fig. 2 is a diagram showing the manner in which the two sections of the movable coil used in my device are energized.

In Fig. l, I show a field coil l1 in diagrammatic fashion only. It is shown as disposed on a. tubular magnetic member l2. This member has an internal flange 13, forming a large 95 central aperture at one end. It can be further provided with an external iiange 14 at the opposite end, against which one end of coil 11 can rest. The exterior of coil 11 is i covered by a tubular magnetic casing 15 fas- 10 hold the piece 17 firmly in centered or central relation to the members 13 and 16.

It is apparent that if, say, thepole piece 16 forms a north pole,the inner edge of flange 18V must form a south pole. The core 1.7 atthat portion opposite the inner edge of pole piece 16 has a south pole induced thereby; and that portion opposite flange 13 has a north pole induced thereby. The course of the lines of force through thecor'e 17 is shown by arrows 19. Thusit is seen that two narrow air gaps are formed; in one, the lines radiate outwardlyv from a north pole (oppositeflange 13); and in the other, the linesconverge .inwardly to a south pole (-oppositepiece 16). Beforeproceeding With a descrip-tion of the moving parts of the mechanism, attention is directed yto the fact that a large interior cool-V ing surface is presented by the interior of tube12. v Consequently the heat energylost in coil 1l can be easily dissipated Without danger of. excessive temperature rise.

Cooperating with the tvvo narrow annular air gaps, are pairV of coils 20, 21, supported on'a thin tube 22 attached to a cone 3. rhis cone can be Vfastened in any appropriate manner at its edges, whereby the Whole movable structure is constrained for axial movement. Then as these coils vare axiallyl moved, the cone Qis actuated to set up corresponding` sound waves.v In order thatthese coils have a cumulative effect on the cone, they must of course carry currents thatfcirculate in oppositedirections because the lines of force in theltivo air gans extend in different direc-y tions. Thus for coil 20, influenced by the gap formed by ilangelfl, currents mustl be supplied that circulate, say, in a clockwise direc-` tion; While for coil 21, influenced by the gap formed by annular member 16, currents must be supplied that circulate in a counterclocltwise direction.y The coils can be supplied fromy a circuit 211 (Fig. 2) that carries the signaling impulses by having one terminal of the rcirrruit connecting toa 'common point 25 for both coils; and the other terminal connects to thev outer terminals of both coils, thus providing a parallel connection for tie coils; and if the coils are Wound in the same directicnvon tube'QQ, the' currents will then circulate in opposite directions. The mag'- netic effects of coils 20, 21 are indicatedby arrows 26, 27,- Vand since both coils are of equivalentnumber vof turns, these-'tivo effectsy .cancel each other. There is thus no kmagnetic ri-.action,y due to these coils on the core.

Preferably, I arrange coils 20 and 21 so as' to be not quite centrally disposed in the gaps When these coils are uneXcited; coil 20,' say, has its medial line passing to the right of the medial line of flange 13; and the coil^2l has its medial line passing to the left of the medial lineof annular member 16. In this Way, When these coils are supplied with current, and if say, they are urged toward the right, then coil 20 tends to move away from its gap, While coil 21 tendstomove into it. The ef- .feetl is that even for very large lovv frequency eurrents,the coils 20, 21 faithfully follow all the modulations without distortion, because the movement of one coil in or out of its field is compensated for by the movement yof the other coil in-an oppositeysense.

f Iclaim:

1. In a dynamic signal reproduce'r, a hollou7 magnetic member, a field coil disposed over the member, an annular pole piece axially'space'd yfrom the end of said member, a core centrallyl ksupported with respect to both'the tubular member and the .annular pole piece toform therewith a pair of; annularair gaps,`a tubular movable support disposed insaid gaps, and al pair vof coils mounted on the support, one in each gap.

2. rIhe combinationas set forth in claim 1,

in Which the coils are so arranged thatl vthe 05 simultaneous axial movements thereof serve to move one furtherinto its field, and to move the other further out of its field. 'o

3, Ina dynamic signal rebroducenaholloivmagnetic. member, a field coil disposed on said member, la casing for the coil,extend infr beyond the hollow member an annular` polle'pi'ece fastened to the casing and axially Aspaced closefto thev end of the hollow member,

are connected to a source of signaling nnpulses in such manner that the forcesl acting on the coils simultaneously are cumulative.

In testimony whereof I lhave hereunto set my hand.` Y

HERMAN il.y .FANGER .les 

